Disappearance of electron-hole asymmetry in nanoparticles of Nd1−xCaxMnO3(x=0.6,0.4): magnetization and electron paramagnetic resonance evidence

Abstract

We study and compare magnetic and electron paramagnetic resonance behaviors of bulk and nanoparticles of Nd1−xCaxMnO3 in hole doped (x=0.4;NCMOH) and electron doped (x=0.6;NCMOE) samples. NCMOH in bulk form shows a complex temperature dependence of magnetization M(T), with a charge ordering transition at ∼250 K, an antiferromagnetic (AFM) transition at ∼150 K, and a transition to a canted AFM phase/mixed phase at ∼80 K. Bulk NCMOE behaves quite differently with just a charge ordering transition at ∼280 K, thus providing a striking example of the so called electron-hole asymmetry. While our magnetization data on bulk samples are consistent with the earlier reports, the new results on the nanoparticles bring out drastic effects of size reduction. They show that M(T) behaviors of the two nanosamples are essentially similar in addition to the absence of the charge order in them thus providing strong evidence for vanishing of the electron-hole asymmetry in nanomanganites. This conclusion is further corroborated by electron paramagnetic resonance studies which show that the large difference in the “g” values and their temperature dependences found for the two bulk samples disappears as they approach a common behavior in the corresponding nanosamples.

Observation of complex magnetic behaviour in calcium doped neodymium manganites

“…For the half doped compound, x = 0.5 composition, the T N is observed at 105 K and a sharp increase in FC curve below 80 K is noticed, which can be accounted to the ordering of Nd sublattices. The results suggest that, upon the substitution of 30-50% of Ca content, the compound changes from pseudo CE-type AFM to CE-type AFM, which is corroborated with earlier reports [21,[34][35][36][37][38][39].…”

“…Upon further increase of Ca content, an additional transition at higher temperature is noticed (shown in figures 3(c) and (d)), which is understood as a charge ordering (CO) transition in accordance with the earlier reports [21]. It is reported that the hole and electron-doped manganites have a tendency of Mn 3+ and Mn 4+ cations to charge and orbital ordering [21]. In the inset to figure 3, M × T versus T is plotted to check the presence of any residual CO in the compounds.…”

“…Recently, the effect of a strong interaction between charge, spin and lattice degrees of freedom was reported in nanoparticles of NCMO (x = 0.2, 0.22, 0.4 and 0.5) by Raju et al [20]. On the contrary, Bhagyasree et al reported a suppression of spin interaction and formation of ferromagnetic layers while reducing the size of samples [21]. To the best of our knowledge, no complete study of the entire Nd 1−x Ca x MnO 3 system has been reported.…”